Disc drives are commonly used in workstations, personal computers, laptops and other computer systems to store large amounts of data in a form that can be made readily available to a user. In general, a disc drive comprises one or more magnetic discs that are rotated by a spindle motor at a constant high speed. The surface of each disc is divided into a series of data tracks which are spaced radially from one another across a band having an inner diameter and an outer diameter. The data tracks extend generally circumferentially around the discs and store data in the form of magnetic flux transitions within the radial extent of the tracks on the disc surfaces. Typically, each data track is divided into a number of data sectors that store fixed sized data blocks.
A read/write head includes an interactive element such as a magnetic transducer which senses the magnetic transitions on a selected data track to read the data stored on the track, or to transmit an electrical signal that induces magnetic transitions on the selected data track to write data to the track. The head includes a read/write gap that positions the active elements of the head at a position suitable for interaction with the magnetic transitions on the data tracks of a disc as the disc rotates.
As is known in the art, each head is mounted to a rotary actuator arm and is selectively positionable by the actuator arm over a preselected data track of the disc to either read data from or write data to the preselected data track. The head includes a slider assembly having an air bearing surface that causes the head to fly over the data tracks of the disc surface due to air currents caused by rotation of the disc.
Typically, several discs are stacked on top of each other and the surfaces of the stacked discs are accessed by the heads mounted on a complementary stack of actuator arms which comprise an actuator assembly, or "E-block." The E-block generally includes head wires which conduct electrical signals from the heads to a flex circuit, which in turn conducts the electrical signals to a flex circuit bracket mounted to a disc drive basedeck. For a general discussion of E-block assembly techniques, see U.S. Pat. No. 5,404,636 entitled METHOD OF ASSEMBLING A DISK DRIVE ACTUATOR, issued Apr. 11, 1995 to Stefansky et al., assigned to the assignee of the present invention.
As will be recognized, a continuing trend in the industry is the reduction in the size of modern disc drives. As a result, the discs in the disc stacks of modern disc drives are increasingly being brought closer together, providing narrower vertical gaps between adjacent discs. This trend toward decreasing size is driving the industry toward smaller heads, longer and thinner actuator arms, and thinner gimbal assemblies. Although these and other size reductions facilitate greater storage capacity, such narrow vertical spacing of the discs and thinning of the actuator arms gives rise to a problem of increased sensitivity of the disc drives to non-operating mechanical shocks.
Non-operating shock, such as encountered during shipping and handling of disc drives, can often cause the heads or actuator arm tips to contact the media on the discs. When a non-operating shock is encountered, the discs and actuator arms vibrate, causing displacement of the actuator arms and discs in a vertical direction (often referred to in the industry as the "Z-axis"). The discs and actuator arms oscillate about the positions they held prior to encountering the non-operating shock. Because the actuator arms have different characteristics than the discs, the oscillation of the actuator arms occurs at a different frequency than the oscillation of the discs. As a result, the wavefunctions for the oscillations of the actuator arms and discs become out of phase, which means that the actuator arms and discs are moving toward each other. If the amplitude of the displacement is large enough, the heads and perhaps even the tips of the actuator arms contact the discs. The resulting contact can damage the surfaces of the discs, the heads, and the actuator arms and has been recognized as a predominant failure mode in modern disc drives.
Although little can be done to completely eliminate contact between the discs and the heads or actuator arms, it is desirable to reduce the amplitude of the force of impact as well as the number of impacts which are encountered for any given non-operational shock. Thus, there is a need for an improved approach to reducing the susceptibility of damage in disc drives resulting from non-operating mechanical shocks.